Electronic scanning antennas are formed from modules positioned in an array. Each module comprises at least one radiating element contributing to the formation of the sending and/or receiving beam. It is known that the direction of the radiated beam is determined by the phase applied to the signal sent or received at each radiating element. Stated otherwise, the direction of the radiated beam is controlled by the phases applied to the radiating elements according to a known law. The modules may or may not be active, the active modules moreover integrating an amplifier of the sent signal.
Thus, an electronic scanning antenna has, for a radar for example, a microwave-frequency architecture consisting of channels comprising, in particular, amplifier modules that may be used for sending and for receiving, which are associated with multifunctional circuits comprising phase-shift elements for aiming the beam in directions other than the normal to the array, each module being equipped with a radiating element.
A drawback of electronic scanning antennas is that they are subject to a misalignment of the radiated beam depending on the temperature. A misalignment such as this is not acceptable with the angular precisions demanded for most radar applications in particular. This misalignment is due to the mechanical deformation of the antenna. More particularly, when the temperature increases, the array structure expands. Conversely, when the temperature decreases, the structure contracts. In any case, the phase controls used for angularly aiming the radiated beam are no longer valid and lead to an aiming error which may be crippling.
A known solution for solving this problem is to carry out a calibration of the electronic scanning array. For this, the operating temperature range of the antenna is sampled, hence between the minimum operating temperature and the maximum operating temperature, and defects of illumination are recorded for amplitudes and phases of the various microwave-frequency channels of the array, a channel being associated with each module of the array. The defects measured during the calibration phase are stored in a table, a so-called calibration table. In the operational phase, the temperature-dependent defects are thus ascertained by reading off the calibration table. At a given temperature, the defect read off the table may thus be corrected by modifying the phase values in order to offset this defect.
A drawback of this solution is that it is tricky and lengthy to implement. Indeed, the measurements must be made for each temperature and copied into the calibration table. The number of measurements is important, as the range of operating temperatures must be sampled sufficiently and the measurements themselves must be made with care on account of the small misalignments involved. Although small, these misalignments may nonetheless impair the precision of detection of a radar.